The present invention relates to cyclone separators such as are used to separate and collect, for analysis, gas- or vapour-borne materials, most usually in the form of particles.
The principle of operation of such a cyclone separator involves the particle-bearing gas or vapour, typically air, being forced tangentially by means of a pressure differential into a cylindrical chamber. The particles, due to their mass are centrifuged to the wall of the chamber and are collected as they fall to the bottom of the chamber, the exhaust air being ducted away from the chamber through an exhaust port.
In one variant of the cyclone separator, a liquid, typically water, is sprayed into the particle carrying inlet air stream, usually just outside the collection chamber. The water droplets are centrifuged with the particles, and wash the collected particles to the bottom of the chamber from where the resulting solution or suspension can be pumped away for use or analysis. This variant is commonly referred to as a xe2x80x9cwetted-wallxe2x80x9d cyclone.
The wetted-wall cyclone may also be used for the collection of analyte material present in the incoming air in the form of air-borne vapours.
The known wetted-wall cyclone, operating with an inlet spray has a functional inefficiency in that, as a result of surface tension effects, the water impacting the wall of the cylone forms clumps and streams rather than a uniformly wetted surface, meaning that the wall washing is invariably of a inconsistent nature and the separation achieved is of variable efficiency.
It is thus one object of the present invention to provide an improved construction of wetted-wall cylone separator.
According to one aspect of the invention a wetted wall cyclone separator is provided with means enabling the inner surface of the wall of the separation chamber to be more uniformly wetted than possible with an inlet spray arrangement, thereby providing a more consistent and more efficient collection of materials introduced into the chamber in the incoming gas or vapour stream than hitherto.
In a preferred embodiment of the invention, the separation chamber has a wall comprised at least in part of a porous material through which a liquid may be forced to provide the more uniform wetting of the inner surface of the cylinder required to achieve the improved consistency and efficiency of sample collection.
The porous material may be a sintered material, for example a ceramic, or a metal, such as sintered stainless steel.
From another aspect the invention consists in a method of separation of a gas or vapour borne material by means of a cyclone separator in which the inner wall of the separator is wetted, and material incoming is collected and carried away by liquid flow across the wall, and in which the liquid is introduced into the separator so as to flow uniformly across the separator wall, thereby to improve the consistency and efficiency of separation.
The liquid may be introduced under pressure through the separator wall, by providing that the wall is at least in part porous.
From a still further aspect the invention consists in an instrument for separating, collecting and analysing gas or vapour borne materials, such instrument comprising a wetted wall cyclone separator in accordance with the present invention.